Comprehensive Geology Study Guide (Chapters 8-14)

Earthquakes

Earth shaking caused by a rapid release of energy, usually due to tectonic forces.

Hypocenter (Focus)

The point within the Earth where fault slip initiates.

Epicenter

The point on the land surface directly above the hypocenter.

Elastic Rebound Theory

Rocks bend elastically under stress; when stress exceeds strength, they rupture, releasing energy.

Fault

Planar breaks in the crust where movement occurs.

Footwall

Block below the fault plane.

Hanging Wall

Block above the fault plane.

Normal Fault

Hanging wall moves down relative to footwall; caused by extension.

Reverse Fault

Hanging wall moves up relative to footwall; caused by compression; steep slope (>30°).

Thrust Fault

Low-angle (<30°) reverse fault common in compressional mountain belts.

Strike-Slip Fault

Blocks slide laterally past each other with no vertical motion.

Fault Trace

Where a fault intersects the ground surface.

Fault Scarp

A small cliff created by displacement at the surface.

Blind Faults

Faults that do not reach the surface.

Stick-Slip Behavior

Friction prevents motion until strain builds enough to cause rapid movement.

Seismic Waves

Energy released during an earthquake travels as waves.

P-waves (Primary)

Fastest seismic waves, compressional (push-pull) motion parallel to wave direction.

S-waves (Secondary)

Slower seismic waves with shear motion perpendicular to wave direction.

L-waves (Love waves)

Surface waves that cause side-to-side snake-like motion.

R-waves (Rayleigh waves)

Surface waves that create a rolling, ripple-like motion.

Seismograph

Instrument that records ground motion during an earthquake.

Seismogram

Data record produced by a seismograph, showing wave arrivals.

Epicenter Location

Determined by the time difference between P and S wave arrivals.

Intensity

Measures shaking/damage severity based on observations (Modified Mercalli Intensity scale).

Magnitude

Measures energy released based on seismogram amplitude.

Richter Scale (ML)

Older magnitude scale, best for nearby earthquakes.

Moment Magnitude (Mw)

Most accurate magnitude scale, especially for large earthquakes.

Intraplate Earthquakes

Less common earthquakes that occur away from plate boundaries.

Ground Shaking

Causes building damage, foundation failure, and collapse.

Liquefaction

Shaking liquefies water-saturated sediments, causing structures to sink.

Tsunamis

Large waves generated by seafloor displacement due to earthquakes.

Prediction (Earthquakes)

Long-term prediction based on identifying seismic gaps and recurrence intervals.

Orogenesis (Mountain Building)

Process of building mountains, involving deformation, metamorphism, and uplift.

Deformation

Changes in rock location, orientation, or shape due to stress.

Strain

Change in shape due to deformation such as stretching or shortening.

Stress

Force applied per unit area in geological contexts.

Brittle Deformation

Characterized by fracturing and faults, occurs in the shallow crust.

Ductile Deformation

Characterized by flowing and folding, occurs in the deeper/hotter crust.

Strike

Compass direction of the intersection of a tilted plane with a horizontal plane.

Dip

Angle of tilt of a tilted plane measured downward from horizontal.

Joints

Planar fractures with no offset that form under tensile stress.

Veins

Fractures filled with minerals that precipitate from hydrothermal fluids.

Folds

Wavelike bends in layered rock, caused by compressional forces.

Anticline

A fold with an arch-like shape where limbs dip away from the center.

Syncline

A fold where limbs dip toward the center, forming a trough.

Cratons

Old, stable continental crust that has survived cycles of tectonic activity.

Radiometric Dating

Determines age in years using the decay of radioactive isotopes.

Half-life

Time required for half of a radioactive isotope to decay.

Fossil Succession

Fossils succeed one another in a known order; used for relative dating.

Unconformities

Time gaps in the rock record due to non-deposition or erosion.

Geologic Time Scale

Calendar of Earth's history based on correlating rock layers globally.